Sectional overhead doors for residential and commercial garages typically have a number of hinged horizontal sections with rollers at each end that run inside tracks extending vertically on each side of the door opening. The tracks continue either vertically or, perhaps most commonly, horizontally inward above the door opening to accommodate the door when in its open position. These doors commonly incorporate a counterweighting system to reduce the effective door weight that must be lifted by a manual or motorized door-opening mechanism.
The components of a typical counterweighting system include an elongate round shaft with a pulley at each end, and at least one helical torsion spring mounted generally concentrically on the shaft. The shaft is rotatably mounted to the building structure above and parallel to the door opening. Each pulley has a door-lifting cable attached to the door at a selected point, typically near the bottom of the door. One end of the spring is non-rotatably fixed to the building structure, and the other end is fixed to a spring cone which in turn is lockably mounted onto the shaft (typically by means of set screws). The spring may be tensioned by rotating the spring cone around the shaft and then locking the spring cone on the shaft. The tensioned spring exerts a rotational force on the shaft, inducing tension forces in the cables, which in turn exert upward forces on the door. These upward forces effectively counteract and reduce the weight that needs to be lifted when operating the door.
There are many known types of spring cones, most of which incorporate a number of radial sockets (typically four) into which steel winding rods can be inserted for purposes of winding the spring cone around the shaft to tension the spring. With the spring cone loose on the shaft, a first rod is inserted into one socket and manual force is applied to the rod to rotate the spring cone and one end of the spring a partial turn, thus increasing spring tension. With the first rod being firmly held (to restrain spring tension), a second rod is inserted into another socket and used to turn the cone further. With the second rod being firmly held, the first rod may be withdrawn and moved to a new socket. This alternating process is continued until a desired spring tension has been achieved, whereupon the spring cone is tightened onto the shaft and the rods are removed from the sockets.
This well-known procedure is effective but potentially dangerous. If the rods are accidentally let go of while the spring cone is loose on the shaft, the tensioned spring will quickly unwind, causing the spring cone to spin on the shaft. If one or both rods are still engaged in spring cone sockets, they will spin rapidly with the spring cone and thus may injure a person standing too close. In fact, the rods may even fly out of the spring cone and thus become dangerous projectiles that can seriously injure or even kill a bystander. The danger inherent in such situations is greater for larger and heavier doors, which typically have heavier springs that store greater potential energy when tensioned.
These risks are particularly great when spring tensioning is being attempted by a single worker. Muscle fatigue and momentary inattention or distraction are only two factors that could cause the worker to lose hold of the winding rods. In view of these concerns, it is less dangerous if the spring tensioning procedure is performed by two workers, each operating only one winding rod. Then if one worker becomes unexpectedly tired or inattentive and loses control of one rod, the other worker will in most cases be holding the other rod safely, and preventing the spring from unwinding. An obvious disadvantage of this safer alternative procedure, however, is that the need for two workers results in higher cost for the spring tensioning operation.
For the foregoing reasons, it is desirable to have spring tensioning methods and means that do not use loose winding rods that can cause injury in case of inadvertent and uncontrolled unwinding of a tensioned spring, and, further, that can be safely by only one worker. The prior art discloses a number of attempts to address this problem. U.S. Pat. No. 2,718,282 (Davis), discloses spring tensioning apparatus having a splined cylindrical member with a longitudinal slot to permit mounting of the member over a spring shaft. The slot is then closed off using a secondary member that slides into longitudinal keyways in the cylindrical member on either side of the slot. The secondary member is also splined so as to create an effectively continuous splined perimeter around the cylindrical member when the secondary member has been positioned in the slot. The cylindrical member has means for connecting to a spring cone so that the spring cone will rotate when the cylindrical member is rotated. Also provided is a pair of pawl-equipped ratchet levers, each having a cylindrical inner surface and an opening to allow positioning over the shaft. The levers are placed over the shaft and slid over the splined cylindrical member, whereupon they may be operated in alternating fashion, with the pawls of the levers engaging the splines of the cylindrical member and causing it to rotate, thus rotating the spring cone and tightening the spring. Because the shaft openings in the levers are smaller than the diameter of the cylindrical member, the levers cannot come free of the cylindrical member without sliding them laterally off of the cylindrical member.
Although being a useful device, the Davis apparatus has several disadvantages. For example, it requires precise machining for splining of the cylindrical and secondary members, as well as for the keyways in the cylindrical member and the corresponding keys of the secondary member. Indeed, if the keyways are not machined to close tolerances, the secondary member will either fit too tightly (thus being difficult to install and remove) or it will be too loose (thus being prone to sliding out of the cylindrical member, making the apparatus inoperable. Even when these parts have been machined to provide an optimal fit, their mating surfaces can become damaged or covered with grime, paint, or other contaminants, in each case making insertion and/or removal of the secondary member difficult or impossible. Furthermore, the secondary member is of necessity a loose component that could be accidentally lost, again making the apparatus unusable.
U.S. Pat. No. 3,651,719 (Wessel) discloses another spring tensioning apparatus that operates on the ratchet principle. This apparatus features an hinged split collar assembly releasably mountable around a spring cone, with a rigid pin that goes into one of the spring cone sockets so that rotation of the collar will cause rotation of the spring cone. The split collar has rounded ratchet teeth around its perimeter, the teeth extending across the full width of the inner collar. The apparatus includes a pair of pawled ratchet handles, each with a hinged split collar section approximately half the width of the toothed inner collar. The Wessel apparatus is operated by opening the inner collar and mounting it to the spring cone, closing the inner collar and locking its hinged sections with an anchor pin, opening the ratchet handle collars of the ratchet handles and placing them over the inner collar, closing the ratchet handle collars and locking their hinged sections together with anchor pins, and, finally, operating the handles in alternating fashion to tighten the spring.
The Wessel apparatus also has disadvantages and drawbacks. Its installation requires the use of three anchor pins, and the loss of even one of these loose components may make the apparatus unusable. It also has several hinges that are prone to wear and breakage that could make efficient use of the apparatus difficult or impossible. Furthermore, installation of the Wessel apparatus on the spring shaft involves a number of steps before it is ready to operate, and these steps must also be performed in reverse in order to remove the apparatus from the shaft after the spring has been tensioned. This comparatively labour-intensive procedure increases the cost of spring tensioning.
Another ratchet-type spring tensioning device is found in U.S. Pat. No. 5,605,079 (Way). This apparatus has a split housing, which is separable for installation onto the shaft and the spring cone, with a bore for receiving the shaft and a number of pins for engaging holes in the winding cone. A split sprocket is integrally mounted to the housing and an annular groove on each side of the sprocket receives a ratchet tool. The ratchet tools are locked into the groove using bolts to prevent disengagement, and are operated in alternating fashion to rotate the sprocket, thus rotating the spring cone to adjust the tension in the spring. Disadvantages of this system include the number of loose components and the higher degree of assembly and disassembly required (i.e. assembly of the split housing and sprocket, attachment of the ratchet tools, and the corresponding disassembly once the adjustment is completed).
In view of the disadvantages of the prior art devices described above, there is a need for an improved apparatus for adjusting the tension of a helically wound torsion spring that has minimal or no small loose components prone to being misplaced, that has minimal hinged components prone to wear and disrepair, and that is simple to attach to and remove from a spring shaft, while being safely operable by a single worker. The present invention is directed to these needs.